1. Field of the Disclosure
The present disclosure relates to a process of halohydrins, more particularly to a process of preparing dichloropropanol (DCP).
2. Description of the Prior Arts
DCP is an important precursor in the synthesis of epichlorohydrin (ECH). After reacting with alkaline substance, DCP is converted into ECH via dehydration and cyclization, so as to obtain the main raw material for the production of epoxy resin or chlorohydrin rubber.
Methods such as high-temperature chlorination of propylene, allyl acetate method, or chlorination of glycerin are conducted to prepare DCP nowadays. The first two methods employ chlorine to undergo an additional reaction of hypochlorous acid, thereby generating large amount of undesired chlorinated byproducts and leading to higher cost for the preparation of DCP.
Chinese Patent Publication No. 101429099 discloses the chlorination of glycerin. Depending on various chlorinating agents, the chlorination of glycerin can be achieved by two different approaches. One adopts gaseous hydrochloric acid, HCl(g), as the chlorinating agent to react with glycerin in the presence of acetic acid to produce DCP. Another approach adopts aqueous hydrochloric acid, HCl(l), as the chlorinating agent to overcome the problems of difficult accessibility or operation limits when using the gaseous hydrochloric acid. However, the second approach needs to feed concentrated aqueous hydrochloric acid in a concentration about 38% into the distillation column continuously, resulting in that larger amount of the hydrochloric acid is consumed in the preparation of DCP. Further, both approaches disclosed in the patent publication require two distillation columns, i.e., a reactive distillation column and a purifying distillation column, to complete the process. The patent publication does not disclose how to purify the overhead product from the reactive distillation column and how to recycle the aqueous hydrochloric acid.
Whatever methods used to prepare the DCP, dichloropropanol-hydrochloric acid solution including DCP, water, and hydrochloric acid are produced during the process. The presence of the triple azeotropic system causes the purification difficulties and complexities, resulting in that DCP and hydrochloric acid cannot be directly separated via the azeotropic distillation.
Chinese Patent Publication No. 101134714 discloses a solvent extraction for purification. Organic extraction solvent is mixed with the dichloropropanol-hydrochloric acid solution and then reacted in a specific extraction equipment to extract the DCP. Although the solvent extraction is capable of extracting 90% of DCP, the extraction cannot be performed as desired unless using the extraction solvent and additional extraction equipment. After the solvent extraction, further purification is also required to remove the extraction solvent from DCP. As a result, the approach in the prior art still costs high and causes lots of pollutions.